稀土Yb对Mg-Zn-Zr镁合金组织及性能的影响

Effect of Ytterbium on the Microstructure and Mechanical Properties of the Mg-Zn-Zr Magnesium Alloys

采用Ta坩埚熔炼法制备Mg-Zn-Zr-Yb镁合金,利用光学显微镜(OM)、扫描电镜(SEM/EDS)和维氏显微硬度仪等分析手段探究了稀土Yb含量对Mg-4%Zn-0.5%Zr-xYb(x=0,0.6,1.2,2.4,4.0)镁合金的显微组织及性能的影响。结果表明:合金中添加Yb元素,可以细化晶粒,当Yb含量为2.4wt.%时,晶粒显著细化,晶粒大小也更为均匀。此外,能谱成分分析发现,稀土Yb在Mg基体中固溶度很小,主要分布在共晶组织中。固溶时效处理后,合金的硬度均有上升。不含Yb元素的镁合金,达到时效峰值的时间为10h;添加Yb元素后,时效峰值时间缩短至3h。且添加2.4wt.%Yb时,时效峰硬度值增加最为明显。

Five Mg-Zn-Zr-xYb (x = 0, 0.6, 1.2, 2.4, 4.0) magnesium alloys were prepared by using a special melting method that the pure elements were sealed in tantalum crucibles and melted in a furnace with the temperature program-controlled. The effect of the ytterbium addition in the alloys on their microsructures and mechanical properties was investigated by using the optical microscope and scanning electron microscope with energy dispersive spectrometer. The experimental results indicated that the grain refinement of the alloys is attained after the addition of ytterbium. Ytter-bium is also useful for the purification of grain boundary. The best grain refining effect was achieved in the alloy with the Yb addition of 2.4 wt.%. The EDS analysis suggested that the ytterbium content in the magnesium matrix is negligibly little. The added ytterbium is present almost wholy in the eutectic mixture. After the solution treatment and aging treatment, the hardness of the magnesium alloys increased. The 125?C aging time for the magnesium alloys without ytterbium to reach the hardness peak is 10 h while those of the Yb-added magnesium alloys are shortened to be about 3 h. The alloy containing 2.4 wt.% Yb has the highest aging hardness peak.